An aerosol is a disperse system in which a solid or liquid is present in very finely divided form in a gas. The aerosol itself is generally produced only upon application using a suitable spray system by the spraying of solutions, emulsions or suspensions, for which purpose e.g. spray cans may be used in which a liquefied compressed gas acts as propellant. When the valve is opened, the propellant/preparation mixture is released through a fine nozzle, and the propellant evaporates leaving the finely divided spray product as an aerosol.
An important technical field for the application of cosmetic aerosol sprays is the field of deodorizing cosmetic products. Common deodorant spray compositions often take the form of anhydrous ethanolic solutions of the deodorizing active ingredient. One disadvantage of these ethanolic solutions is a skin-irritating effect in persons with a relevant predisposition having sensitive skin. Likewise on skin that has been mechanically irritated by shaving, application of the common ethanolic solutions leads to a very unpleasant burning sensation. A further disadvantage of ethanolic solutions is that the incorporation of aqueous or water-soluble active ingredients, in particular of antiperspirant or deodorant active ingredients or hair growth inhibiting active ingredients which are not also soluble in ethanol, can be achieved only to a limited degree or not at all.
As an alternative presentation to the ethanolic solutions, anhydrous suspensions of the powdered sweat-reducing active ingredient, usually an aluminum salt, in addition to the propellant in a liquid carrier, usually a relatively volatile oil such as cyclomethicone, are discussed in the prior art. Before spraying, the suspension must be shaken. One disadvantage of these suspension aerosols is the risk that the valve or nozzle apertures become blocked when relatively high concentrations of the salt are used. Attempts have therefore been made to spray the antiperspirant salt in dissolved form. However, the packaging of aqueous antiperspirant salt solutions in propellant-containing metal cans causes serious corrosion problems in aerosol packaging, so that even with lacquered spray cans, corrosion phenomena inevitably occur on the can.
As another alternative presentation, the prior art describes water-in-oil emulsions (W/O emulsions). For instance the German patent application DE 10 2006 062 499 A1 (Henkel) describes a W/O emulsion which is suitable as an aerosol spray. The emulsions disclosed in this application contain cyclomethicones, however. Cyclomethicones have excellent performance characteristics, particularly in terms of emulsion stability, and for this reason they are widely used in cosmetics and particularly in antiperspirants. However, with too high a proportion of volatile cyclomethicones, after drying, i.e. some time after application, antiperspirants form white residues on the skin, which do not adhere well to the skin and are perceived by the user as unpleasant, particularly if they are transferred to dark-colored clothing.
There is therefore a need for a stable water-in-oil emulsion suitable for use in an aerosol spray with a low cyclomethicone and ethanol content. The emulsion should, in addition, be distinguished by a low corrosion tendency when stored in a metallic spray can and by a good cosmetic, particularly antiperspirant, action and low residue formation upon application. Furthermore, the cosmetic active ingredient should be released particularly well from the W/O formulation.
Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.